Spiral Slot Research Articles

Supercritical Antisolvent Micronization of Natural Carotene by the SEDS Process through Prefilming Atomization

Natural carotene is micronized by the SEDS process through prefilming atomization (SEDS−PA) with the aim of evaluating the efficiency of prefilming atomization, examining the variation of carotene purity induced by the SEDS−PA process and studying the influence of operating variables on the particle size (PS) of the carotene precipitates. The carotene/dichloromethane solution to be atomized is driven through a liquid distributor with spiral slots in the prefilming atomizer as a thin film swirling at 45°. At the exit of the atomizer, the atomizing supercritical CO2 (SC-CO2) stream impinges on the film at 45°. Through the impingement and the use of swirling, the annular solution film is disintegrated into fine drops, and the mixing of the SC-CO2 and solution is intensified. Compared to the process in which solution is driven through the inner capillary of the atomizer while SC-CO2 is driven through its annular passage, the SEDS−PA process can obtain smaller droplets and finer microparticles with a narrower particle size distribution (PSD). After micronization by the SEDS−PA process, the purity of carotene microparticles is increased for unprocessed carotene with purity ranging from 30% to 87%, but it decreased for carotene with purity higher than 87%. The CO2 flow rate, solution flow rate, solution concentration, and pressure have marked influences on the particle size (PS), and the PSD broadens with increasing PS. Mechanisms that control PS are explained in terms of liquid atomization, agglomeration of particles, volumetric expansion of solution in SC-CO2, and nucleation and growth processes of particles. The dependence of the PS on temperature is not clear from all of the experiments performed.

Breakdown characteristics of Z continuous winding in HTS transformer

For the development of electrical insulation design of a HTS transformer with Z continuous winding, we have discussed insulation composition and investigated breakdown characteristics such as breakdown of LN 2, polymer and surface flashover on FRP and breakdown-surface combination in LN 2. Also we have designed and manufactured a bobbin that has spiral slot for the Z continuous winding. A Z continuous winding mini-model from Kapton film insulated Cu tape for simulated 22.9 kV class HTS transformer has been constructed using 0.1% breakdown strength obtained by Weibull distribution. The winding model was measured with respect to its insulation characteristics such as ac (50 kV, 1 min) and impulse (154 kV, 1.2 × 50 μs full wave, 3 times) withstand test and its excellent performance was confirmed.

The quasi-static response of compliant prosthetic sockets for transtibial amputees using finite element methods

The finite element method (FEM) is a very powerful tool for analyzing the behavior of structures, especially when the geometry and mechanics are too complex to be modeled with analytical methods. This study focuses on the analysis of patellar tendon bearing prosthetic sockets with integrated compliant features designed to relieve contact pressure between the residual limb and socket. We developed a FEM model composed of a socket, liner and residual limb and analyzed it under quasi-static loading conditions derived from experimentally measured ground reaction forces. The geometry of the residual limb, liner and socket were acquired from computed tomography (CT) data of a transtibial amputee. Three different compliant designs were analyzed using FEM to assess the structural integrity of the sockets and their ability to relieve local pressure at the fibula head during normal walking. The compliant features consisted of thin-wall sections and two variations of spiral slots integrated within the socket wall. One version of the spiral slots produced the largest pressure relief, with an average reduction in local interface pressure during single-leg stance (20–80% of the stance phase) from 172 to 66.4 kPa or 65.8% compared to a baseline socket with no compliant features. These results suggest that the integration of local compliant features is an effective method to reduce local contact pressure and improve the functional performance of prosthetic sockets.

Design optimization of micromachined ferroelectric-based phase shifter using modified ground coplanar waveguide

In this paper, a new approach to optimally design a phase shifter consisting of a periodic array of ferroelectric-based tunable planar interdigital capacitors (IDCs) is presented. Spiral slots in the proposed configuration reduces the overall size and improves the performance by 30%.

Rectangular increasing distance spiral slots (RIDSS) PBG applied to MEMS frequency-reconfigurable antenna design

A frequency-reconfigurable antenna with rectangular increasing distance spiral slots (RIDSS) PBG, which is controlled by two microelectromechanical systems (MEMS) switches, is presented. The antenna can work at four states (in the 32–36-GHz band) with different configurations of the switches. The RIDSS PBG structure can restrain the leakiness of RF energy through DC control of the feed lines of the switches. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 394–395, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21179

Novel compact photonic bandgap structures using rectangular increasing‐distance spiral slots

AbstractA novel and compact rectangular increasing‐distance spiral slots (RIDSS) structure has been proposed for photonic bandgap (PBG) applications. The dimension of the RIDSS structure is only about 1/8λ at the cutoff frequency. Only three cells of the RIDSS‐PBG are sufficient for the measured >20‐dB stopband from 1470 to 2034 MHz, thus rendering the whole structure super‐compact. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 537–539, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20527

Novel compact photonic band‐gap structures using rectangular increasing‐distance spiral slots

AbstractA novel, compact, rectangular increasing‐distance spiral‐slot (RIDSS) structure is proposed for photonic band‐gap (PBG) applications. The dimension of the RIDSS structure is only about 1/8λ at the cutoff frequency. Only three cells of the RIDSS‐PBG are sufficient for the measured beyond the 20‐dB stopband from 1470 to 2034 MHz, thus rendering the whole structure super‐compact. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 144–146, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20402

Precipitation of ephedrine by SEDS process using a specially designed prefilming atomizer

One of the key processes of SEDS precipitation is droplet formation due to jet break-up at the exit of an injection device. In this work, a prefilming atomizer was designed on the basis of the mechanisms of atomization and applied to the SEDS process to precipitate ephedrine from ethanol solution using supercritical CO 2 as antisolvent with the aim of evaluating the efficiency of the atomizer and studying the influence of operating variables (concentration, pressure, temperature, solution flow rate, and CO 2 flow rate) on sizes of the particles micronized. The solution to be atomized was driven through a coaxial annular passage with spiral slots in the atomizer as a thin film swirling with 45°. The atomizing CO 2 was driven through another passage (the inner capillary) to form a jet stream to impinge on the film at 45°. Upon violent interaction with jet streams, the solution sheet was effectively disintegrated into fine drops and the mixing of supercritical fluid (SF) and solution was intensified for increased transfer rates. Long needle-like or short rod-like uncoagulated particles were obtained by the SEDS process in a wide range of experimental conditions. The mechanisms that control particle sizes were explained in terms of liquid atomizing mechanism, nucleation, and growth processes of particles. Particle size did not seem to depend on pressure and temperature in all the experiments performed.

ANALYSIS OF CIRCULARLY POLARIZED DIELECTRIC RESONATOR ANTENNA EXCITED BY A SPIRAL SLOT

The hemispherical dielectric resonator antenna (DRA) excited by a single-arm spiral slot is studied theoretically in this paper. The Green’s function technique is employed to formulate an integral equation for the spiral slot current. The moment method with piecewise sinusoidal (PWS) basis and testing functions is used to convert the integral equation into a matrix equation by using a deltagap exciting source. The input impedance, return loss, axial ratio and radiation pattern are calculated. Numerical results demonstrate that the analysis is efficient.

Studies of the novel CPW-fed spiral slot antenna

The design and analysis of a coplanar waveguide-fed spiral slot antenna, applied in most of the commercial wireless communication systems, have been proposed and presented in this paper. The spiral slot antenna and the feeding structure are fabricated on the same plane of the substrate so that the circuit process and the position alignment could be simplified. The comparisons of the measured initial operated frequency versus the substrate thickness, the turn number and the slot width are detailed and discussed.

DESIGN OF CIRCULAR POLARIZED RADIAL LINE SLOT ANTENNAS

A systematic design process for circular polarized radial line slot antennas is presented herein. In order to obtain circular polarization a spiral slot arrangement is needed. Slot coupling determination to obtain a desired aperture illumination is also important. The unit radiation element is composed of two slots that are designed to optimize the copolar to crosspolar ratio and the position and length of all the slots in the array can be determined with this method. Although the suggested method is suitable for obtaining any high or medium gain antenna, a direct broadcast satellite (DBS) reception antanna design is proposed as an application example.

A frequency-reduction scheme for spiral slot antenna

We present a new technique to reduce the initial resonant frequency, enhance the bandwidth, and miniaturize the antenna size for microstrip-feeding spiral slot antennas. Two spiral slot antennas were fabricated and measured to demonstrate the capability of lowering the initial resonant frequency by adding a circular capacitive stub at the end of the feedline. According to results, the initial resonant frequency of the proposed antenna has been shifted from 1.58 to 1.28 GHz; in other words, the antenna size can be reduced by 20%, approximately. The radiation patterns are simulated and measured at 1.3 GHz and 3 GHz to examine the excitation mode. The variations of the initial resonant frequency versus the radius of the circular stub are also shown to find the optimum radius of the stub.

Circularly polarized rectangularly bent slot antennas backed by a rectangular cavity

Rectangularly bent slot antennas backed by a rectangular cavity for circular polarization are proposed. Characteristics of three types of cavity-backed rectangularly bent slot antennas for circular polarization-the single square loop slot, the two-element square loop slot, and the two-arm square spiral slot antenna-are analyzed numerically. The generalized network formulation based on the equivalence principle is given in terms of the method of moments. The magnetic currents on the thin rectangularly bent slots in the presence of the backing cavity are obtained and used to calculate the input impedance, radiation pattern, and axial ratio. Experimental results on the input impedance, radiation pattern, and axial ratio are in good agreement with calculated data.

Analysis of thin multioctave cavity-backed slot spiral antennas

Thin cavity-backed Archimedean slot spirals are analysed through an efficient implementation of the finite element method. Through numerical analysis, fundamental differences between the free-space and cavity-backed configurations are identified. The bandwidth limitation imposed by the presence of the cavity is remedied by terminating the spiral slot with tapered resistive loading and employing larger apertures. Design improvements are presented based on the interpretation of the numerical simulations. It is shown that a 0.8 cm (0.33 in) thick and 24 cm (9 in) wide antenna can provide circular polarisation over a nearly 4:1 bandwidth.

Stripline-fed printed square spiral slot antennafor circular polarisation

A novel design for a circularly-polarised printed square spiral slot antenna with a stripline feed is demonstrated. The printed slot antenna consists of a square spiral slot of /spl sim/1.25 turns, and a total slot length of approximately one free-space operating wavelength. By carefully trimming both ends of the square spiral slot, circular polarisation (CP) operation with a wide operating bandwidth can easily be achieved. A CP bandwidth of >6% has been obtained.

Stripline-fed arbitrarily shaped printed-aperture antennas

A full-wave analysis method is presented for modeling the radiation properties of a stripline-fed planar printed-aperture antenna element. In this formulation, both the finite length of stripline and the finite aperture may be of any arbitrary shape since their equivalent electric and magnetic currents are modeled with triangular patch basis functions. Galerkin's method is applied to numerically solve the coupled mixed-potential integral equation (MPIE). Exact spatial-domain Green's functions are used to account for all radiation, surface-wave, and mutual-coupling effects. Interactions between the stripline feed and the radiating aperture are rigorously included. Numerical analysis is presented for the following nonrectangular shapes: an exponentially tapered slot, an annular slot, an annular slot with opposing stubs, and a monofilar Archimedean spiral slot element. Results are shown for input return loss, radiation patterns, and axial ratio for the circularly polarized elements.

Monofilar Archimedean Spiral Slot Antennas

ABSTRACT A monofilar Archimedean spiral is adopted as a circularly polarized slot radiator which is electromagnetically coupled to a feed line. Numerical analysis of the coupling between the slot and the feed line reveals that, when the slot arm length is properly chosen, a traveling-wave magnetic current is distributed along the slot, leading to the radiation of a circularly polarized wave. On the basis of this radiation mechanism, a spiral slot printed antenna fed by a triplate transmission line is experimentally designed to obtain a unidirectional radiation beam. It is found that an axial ratio of 0.6 dB is achieved, and that the spiral slot is matched to the transmission line with a VSWR of less than 1.5. An array antenna composed of 32 printed spiral slots is constructed, attaining a 5 % bandwidth for a 3-dB axial ratio criterion. The formation of several tilted beams is also demonstrated.

Single-arm spiral slot antenna fed by a triplate transmission line

A spiral slot antenna consisting of a single arm is etched into the upper plate of a triplate transmission line. Power on a feed strip line located between the upper and lowe plates of the triplate is electromagnetically coupled to the spiral slot. The configuration of the spiral slot is optimised for radiation of a circularly polarised wave. An array antenna consisting of spirals slots, to which a pair-element technique is applied, shows wideband characteristics for the return loss and axial ratio.

Discussion of “ Analysis of Spiral Vortex and Vertical Slot Vortex Drop Shafts ” by Michael C. Quick (March, 1990, Vol. 166, No. 3)

Discussion of “ <i>Analysis of Spiral Vortex and Vertical Slot Vortex Drop Shafts</i> ” by Michael C. Quick (March, 1990, Vol. 166, No. 3)

Discussion of “ Analysis of Spiral Vortex and Vertical Slot Vortex Drop Shafts ” by Michael C. Quick (March, 1990, Vol. 166, No. 3)

Discussion of “ <i>Analysis of Spiral Vortex and Vertical Slot Vortex Drop Shafts</i> ” by Michael C. Quick (March, 1990, Vol. 166, No. 3)